1. Field of the Invention
The present invention relates to a reinforcing configuration of an optical guide plate used in a liquid crystal display (LCD) panel, etc., and relates to a displaying unit, an optical guide plate, and information device preventing distortion due to changes in temperature and humidity of use environment.
2. Description of the Related Art
A displaying unit using an LCD panel, etc. has a configuration as shown in FIG. 1, for example. This displaying unit 2 is disposed with an optical guide plate 8 on a backside (non-display side) of a display panel 4 along with a plurality of films 6 therebetween and is disposed with a light source 10 on a side surface of the optical guide plate 8. The light source 10 is surrounded by a reflector 12 to limit a radiation direction of light 14. The light 14 is radiated through the optical guide plate 8 to the backside of the display panel 4. The optical guide plate 8 is an optical guide member that includes a reflecting surface 18 composed of an inclined surface configured with a thicker light entrance portion 16 and a thinner opposite side surface to guide the light 14 from the light source 10 to the backside of the display panel 4 efficiently and uniformly. The displaying unit 2 is disposed with a control substrate 20, a driver IC 22, etc. used for display control.
Such a displaying unit 2 is used in various display apparatus, for example, built into a displaying unit of a portable personal computer and used for information display, and is required to be thinner and lighter. Upon such a request, the optical guide plate 8 is formed as a thin plate and, for example, an acrylic plate is used. If the optical guide plate 8 is formed thinner, the rigidity of the optical guide plate 8 is reduced, and distortion such as expansion and curvature are easily generated depending on changes in environmental temperature and humidity. If the distorted optical guide plate 8 comes in contact with glass cells of the display panel 4, the liquid crystal displays and the outer shape of the displaying unit 2 are affected. For example, as shown by a dotted line a of FIG. 1, if the optical guide plate 8 warps toward the display panel 4, comes in contact with the cells of the display panel 4, applies stress due to the distortion from the optical guide plate 8 to the display panel 4, and changes the gaps of the liquid crystal layer of the display panel 4, the display is affected and the display quality may be reduced. Therefore, the optical guide plate 8 is designed and fabricated so as to warp toward the rear surface, as shown by a dotted line b of FIG. 1. Such a distortion toward the rear surface generates changes in the outer shape of the displaying unit 2.
With regard to the prevention of such a distortion of the displaying unit, prior arts include Japanese Patent Application Laid-Open Publication Nos. 1992-56822 and 1998-10325.
In a liquid crystal display apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 1992-56822, for example, as shown in FIG. 2, a main frame 24 is disposed to surround the peripheral edge of the optical guide plate 8; a plurality of reinforcing frames 26, 28 are disposed between the upper edge and the lower edge of the frame 24; and the frame 24 is reinforced by the reinforcing frames 26, 28 to prevent the distortion of the optical guide plate 8. Since each reinforcing frame 26, 28 is fixed to the frame 24 with screws and has a relatively wide bar shape as shown in FIG. 3, while the frame configuration is strengthened, a thickness t of the optical guide plate 8 and the reinforcing frame 26 (or 28) is increased because the reinforcing frame is disposed in the thickness direction of the frame 24, and the displaying unit 2 is prevented from being thinner and lighter. In the case of the displaying unit 2 not using the frame 24, the reinforcing frames 26, 28 cannot be disposed for reinforcing the frame 24.
In the reinforcing configuration of disposing and closely attaching the wide bar-shaped reinforcing frames 26, 28 to the back surface of the optical guide plate 8, the back surface of the optical guide plate 8 is covered by the reinforcing frames 26, 28 as shown in FIG. 4, and the proportion of the reinforcing frames is increased, although a degree of the reinforcement of the frame 24 is improved, the placement of the control substrate 20 and the driver IC 22 is limited on the back side of the optical guide plate 8 and a degree of freedom is reduced in the design of the control substrate 20, etc. As shown by a dotted line in FIG. 4, the driver IC 22 cannot be disposed in the portions covered by the reinforcing frames 26, 28.
Referring to a backlight apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 1998-10325, for example, as shown in FIG. 5, the rigidity of the optical guide plate 8 is increased by embedding a reinforcing plate 30 in the optical guide plate 8. While the reinforcing plate 30 is located in a direction orthogonal to a cold-cathode tube 32 that is a light source in this case, the reinforcing plate 30 embedded in the optical guide plate 8 affects the propagation of the light 14 in the optical guide plate 8 and generates deflection 34 such as unevenness or shade in the diffusion of the light 14. This affects the liquid crystal display and causes reduction of the display quality. This is caused because the reinforcing plate 30 in the optical guide plate 8 blocks the light 14 and prevents the diffusion of the light 14. Even when the rigidity of the optical guide plate 8 is increased by disposing the reinforcing plate 30 in this way, if the reinforcing plate 30 causes the reduction of the display quality, the disposal of the reinforcing plate 30 has little practicability.
Although techniques of prevention countermeasures for the distortion of the optical guide plate 8 are disclosed for preventing the distortion of the optical guide plate 8 indirectly by disposing the reinforcing frames 26, 28 or for preventing the distortion by embedding the reinforcing plate 30 in the optical guide plate 8 to enhance the rigidity of the optical guide plate 8 directly, a problem is generated when making the display unit 2 be thinner and lighter; the problem is not disclosed with regard to the prevention of the distortion of the optical guide plate 8 while ensuring a degree of freedom of the disposal of the control substrate 20 and the driver IC 22 on the back side; and the techniques disclosed in Japanese Patent Application Laid-Open Publication Nos. 1992-56822 and 1998-10325 cannot solve such a problem.